Unless the holiday is in a major city where all the usual customs apply, the ideal clothing for a not-too-hot holiday in my opinion is a safari jacket over fresco trousers worn with saddle shoes. The combination has it all. The jacket has plenty of pockets for everything from passport to sunscreen. It can be worn over a polo or a tee, and dressed up with a scarf when the occasion calls for it. Or not. The trousers wear cool and resist wrinkles, and the saddles keep looking good with polish or without.
With those in hand man needs little more than a duffle with his underwear, swimwear and a change of shirts; a companion; a straw hat; a motor scooter and a locale like the Mayan or Amalfi coast.